Joint Pilot Placement and Symbol Design Scheme for Sparse Channel Estimation in OFDM systems

Most existing works on the deterministic pilot design for sparse Channel Estimation (CE) in Orthogonal Frequency Division Multiplexing (OFDM) system are based on the assumption that the pilot symbols are equally-powered. This assumption may not necessarily exhibit low coherence compressed CE. This, therefore, calls for the optimization of pilot symbols and their placement which in the literature is considered as a disjoint optimization problem. In this paper, the joint pilot placement and symbol design optimization problem for sparse CE in OFDM systems is considered based on minimizing the mutual coherence of the Fourier submatrix associated with the pilot subcarriers. In order to avoid the disjoint optimization of the pilot symbol values and their placements, a joint pilot placement and pilot symbol design scheme is proposed that optimizes over both the pilot symbol values and their placements as a single design optimization problem. Simulation results demonstrate that the proposed scheme is effective and offer a better CE performance - in terms of Mean Square Error (MSE) and Bit Error Rate (BER), when compared to former pilot placement schemes that assume the equally powered pilot symbols and other schemes that jointly design the pilot symbols and their placement. It was also observed that the proposed scheme can realize 18.75% improvement in bandwidth efficiency with the same CE performance compared with the least squares (LS) CE.